| Epoxy resin(EP)has the advantages of low curing shrinkage,high adhesive strength and resistance to hydrolysis,and is thus widely used in aerospace,adhesives,architectural coatings and microelectronics.However,EP is extremely flammable,it not only threaten the safety of people’s life and property but also limits its application in much more high-tech fields.Therefore,it is necessary to improve its flame retardancy.In this thesis,three DOPO-based flame retardants(FRs)were synthesized from the perspective of molecular design of three-in-one compounds containing P/N/S.Using 4,4’-diaminodiphenylmethane(DDM)as the curing agent,three kinds of flameretarded epoxy resin composites(FREPs)were prepared and their thermal stability,flame retardancy,mechanical properties,transparency properties and flame retardant mechanism were systematically investigated.The specific studies are as follows.(1)A new bio-based flame retardant(AVD)was synthesized by a simple one-pot method using 9,10-dihydro-9-oxa-10-phosphafi-10-oxide(DOPO),vanillin(VN)and 2-aminobenzothiazole(ABT)as raw materials.The FREPs with different AVD contents were prepared using DDM as the curing agent.In the case of the AVD loading level of 7.5 wt.%,the modified epoxy resin passed the UL-94 V-0 test grade with the LOI value of 31.3%.Meanwhile,the PHRR,THR and TSP of EP/7.5 wt.% AVD decreased by 54.7%,14.7% and15.4% as compared with pure EP,respectively.It indicates that the modified EP has better fire safety.(2)A flame retardant(named as DOPT)with active secondary amine groups was synthesized by the Atherton-Todd reaction between DOPO and ptoluenesulfonamide(PTSA).FREPs with different DOPT contents were prepared using DDM as the curing agent.At loading level of 5.0 wt.% DOPT,the FREP reached UL-94 V-0 rating with the LOI value of 37.5%.Compared with pure EP,the PHRR,THR and TSR of EP/5 wt.% DOPT composites decreased by 68%,23.3% and 25.9%,respectively.In addition,the compatibility of DOPT and EP was improved through the interaction between the reactive amine group of DOPT and epoxy group of EP,and the optical transparency of the FREP was maintained.Importantly,the mechanical properties were also enhanced,i.e.,the tensile strength increased by 10.2%and the bending strength rose by 109%.(3)A Schiff base intermediate was produced from vanillin(VN)and ptoluenesulfonamide,and a bio-based intrinsic flame retardant(DOVNPT)was further synthesized by reacting the P-H bond in DOPO with the C=N bond of the intermediate.DOVNPT acted as co-curing agent of DDM due to its active secondary amine group.The incorporation of merely 4.0wt% DOVNPT endowed the FREP with UL-94 V-0 rating and LOI value of 34.4%.Meanwhile,the release of heat and smoke was also significantly suppressed,and the PHRR and THR values decreased by 40.4% and 24.8%,respectively,as compared with those of pure EP.In addition,the compatibility between DOVNPT and EP was improved since the DOVNPT participated in the curing process of EP,the FREPs thus kept a good transparency and an enhanced mechanical properties.Its transparency maintained 97.6% of the pure EP,and its tensile and flexural strengths are improved by 12.7% and 23.1%,respectively. |
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